Wireless transmit/receive units (WTRUs) may perform intra/inter-frequency and inter-radio access technology (inter-RAT) measurements for mobility purposes. Intra-frequency measurements may be performed by the WTRU on the same carrier frequency as its current serving cell. The WTRU may carry out such measurements without measurement gaps. Inter-frequency neighbor or cell measurements may be performed by the WTRU on a carrier frequency different from the current serving cell. The WTRU may not to be able to carry out such measurements without measurement gaps. Measurement gaps may be periods during which the WTRU may not make or receive any transmissions on the frequency of the serving cell. Inter-RAT measurements may be performed by the WTRU on a carrier frequency used by another RAT, perhaps other than the one that may be used by the WTRU in the current serving cell.